Embolization devices in the form of coils where the wire body is formed by a thread extending helically around the center line of the wire body are well-known within radiology, where embolization coils are used for a number of different purposes all with the common feature that it is desired to limit or stop the free flow of blood in an area of a blood vessel. As examples of endovascular fields of application for embolization devices for percutaneous, transluminal insertion using minimally invasive techniques can be mentioned occlusion of an aneurism to prevent rupture of the vessel wall with resulting bleeding. Aneurisms may occur anywhere in the vascular system, but particularly cerebral and abdominal aneurisms require treatment to avoid life-threatening conditions. Another application is occlusion of arteriovenous malformations (AVM), where short-circuiting of arteries and veins looking like skeins of wool may occur, or occlusion of arteriovenous shunts or fistulas, which are major short-circuits between the artery side and the vein side in the vascular system with resulting heavy undesired blood flow. A fourth example of an application is blocking of the blood flow to a tumor, and a fifth, closure of traumatically conditioned blood flows owing to incised wounds or other bodily injuries or gastrointestinal bleeding.
Since embolization devices can be used in many different places in the vascular system and in vessels with very differing sizes, many different coils have been specially designed with various basic designs of the predetermined shape, and each basic design is usually made in a number of different sizes. To treat emergency patients, radiologists today have to stock a large number of different coils, and in the endovascular repair normally many coils are used which are inserted individually and are placed in a pile at the site of placement to be occluded. Considerable expertise is required to select the correct coil sizes for the relevant application, and the risk of unintended migration of a coil to other vessel sites owing to insufficient fitting within the vessel cannot be disregarded.
Conventionally, the predetermined shape of the embolization devices is made so that the wire body is helical with a helix diameter of the same size or slightly larger than the relevant vessel lumen, so that the wound wire body exerts an abutment pressure against the vessel wall. If the helix diameter is too large, the pressure against the vessel wall may become injuriously high, and if it is too small, the wire body can easily be released and drift away. Embolization coils with a regular helical shape or irregular coil shape are known from, for example, U.S. Pat. No. 4,994,069, U.S. Pat. No. 5,122,136, WO94/11051 and WO94/11051; SU-1777842-A1 discloses a coil with a single helix, WO95/25480 describes a spiral coil, DE-295 18 932-U1 a spherical coil, and WO96/18343 and U.S. Pat. No. 4,994,069 coils with a random matrix shape.
Before insertion of the embolization device, a catheter is placed transluminally in the vascular system having its distal catheter end at the site of placement, whereupon a guidewire mounted with the embolization device is pushed in through the catheter. When the wire body leaves the distal end of the catheter, it seeks to assume the predetermined shape. If the size and shape of the device are deemed suitable for the vessel geometry at the site of placement, the wire body is disconnected from the guidewire. A number of applicable types of coupling means in the back end of the guidewire with associated corresponding part on the guidewire are known, see for example EP-A-720 838 disclosing a screw thread, U.S. Pat. No. 5,217,484 disclosing a prehensile claw, WO94/06503 disclosing a pin connection, WO94/06502 disclosing a clamp connection, WO96/00104 disclosing a conical thread connection and EP-A 717 969 disclosing an inflatable holder.